Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$51.49	8.522%	$55.878	$55.88	$55.90	$55.90
Purchase #2	$29.99	10.297%	$33.0781	$33.08	$33.10	$33.10
Purchase #3	$223.41	4.786%	$234.1024	$234.10	$234.10	$234.10
Purchase #4	$161.61	7.859%	$174.3109	$174.31	$174.30	$174.30
Purchase #5	$99.52	6.112%	$105.6027	$105.60	$105.60	$105.60
Purchase #6	$146.50	8.381%	$158.7782	$158.78	$158.80	$158.80
Purchase #7	$65.76	13.581%	$74.6909	$74.69	$74.70	$74.70
7 purchase totals =	$778.28		$836.4412	$836.44	$836.50	$836.50